Pulping processes



PULPING PROCESSES 2 Sheets-Sheet l Filed April 8, 1960 Sept. 1, 1964 PULPING PROCESSES Filed April 8, 1960 W. B. SIMMONS ETAL 2 Sheets-Sheet 2 United States Patent O 5,147,79 lPULllNG PROCESSES Wiiiiam B. Simmons, Leo G. Sheaiy, Roy C. Garrett, and William l. Shannon, all of Port St. Joe, Fla., assrgnors to St. .loe Paper Company, Jacksonville, Fla., a corporation of Florida Filied Apr. 8, 1960, Ser. No. 26,923 lll Claims. (Cl. 162-76) This invention relates to processes for pulping fibrous ligno-cellulosic materials, and more particularly to digestive treatments of such materials in aqueous digesting liquors.

A general object of the invention is to provide improvements in pulping processes involving the digestive treatment of ligno-cellulosic materials in liquors which contain soluble sulfur compounds as components thereof.

A speciiic object is to provide improvements in the kraft or sulfate process which improve the brightness and color characteristics of the pulps produced in accord therewith.

Another speciic object is to provide improvements in the sulfate process which increase the strength of the pulps produced thereby.

Another specific object is to provide improvements in the soda processes which employ sulfur compounds as components of the digesting liquors, the object of the improvements being to improve the brightness characteristics of the pulps produced in accord therewith.

Another specific object is to provide improvements in neutral sulfte type processes for pulping woods, the object of the improvements being the production of unbleached pulps having better brightness characteristics.

Still another object of the invention is to provide improvements in wood pulping processes which reduce the loss of strength that normally accompanies the aging of paper prepared from pulps produced in accord with such processes.

Another object of the invention is to provide a process for pulping wood wherein foaming during the wood digest stages is appreciably reduced, and accordingly wherein the liquor holding capacity of the digester during the digesting stage may be substantially increased without loss of liquor through the removal of foam during the bleeding of the gases and turpentine from the digester.

The alkaline processes which are most widely employed for producing paper pulp are the so-called kraft or sulfate process and the soda process. The former process involves the use of digestion liquors which contain sodium hydroxide and sodium sulfide as the active digesting components of the liquor. On the other hand, the soda process as it is operated today in most mills is actually a modified process since the liquors employed for digestion not only contain sodium hydroxide in accord with the original plan behind the process but also contain small quantities of sodium sulfide as an active component of the liquor. The use of the sodium sulfide in the liquors of the original soda process has been found to impart greater strengths to the pulps produced with the alkaline process.

The alkaline processes for the production of wood pulp by treatment of wood with alkaline liquor containing sodium sulfide generally involve a preliminary step wherein the wood is prepared for digestion. The preparation includes a de-barking operation in which the bark is removed from the logs and further includes a chipping or shredding operation in which the logs are shredded or cut into chips of a suitable small size to facilitate their digestion. Thereafter the chips or shreds are digested in caustic liquor containing sodium sulfide under elevated pressures and temperatures to separate by dissolution, as completely as practical, the lignin content from the cellulosic fibers of the wood. During the digestion period such turpentine oils as are contained in the wood are volatili/Zed and usually removed from the digester together with noncondensable gases found therein. After a suitable digestion period the pressure is released as the contents of the digester is passed to blow tanks. This action breaks down the chips or shreds into a form of wood pulp and thereafter the pulp is refined in suitable mechanical breakers. Subsequently the pulp is separated from the caustic liquor and washed, as for example, on conventional drum type rotary filters. The washed pulp is then screened to separate undigested chips, shreds, shives, etc. from the pulp. produced. The washed and screened pulp is then employed in the production of paper either with or without prior bleaching depending upon the type paper to be produced. The Wash water diluted caustic liquor, i.e. the black liquor, is subjected to suitable treatments for the recovery of its contained alkali content. ln most sulfate processes a portion of the black liquor is recycled and combined with the white liquor fed to the digestion stage of the process. This is done to dilute the white liquor and to utilize the heat content of the black liquor. However, in other versions of the sulfate process as reported in the literature all of the black liquor is subjected to a chemical recovery process and white liquor is employed as the sole digesting medium.

The recovery of the chemical content of the black liquor is carried out by first evaporating the black liquor to a suitable high solids content, after which the liquor is burned in a suitable furnace to transform the caustic content thereof to a causticizable form, i.e. sodium carbonate. The sodium carbonate-containing-smelt formed in the furnace is thereafter leached, and the leach liquor is treated with lime to causticize, and thereby transform, a substantial portion of the dissolved sodium carbonate to caustic soda. The causticizer effluent is generally termed white liquor and is employed, after the separation of the lime mud, for digesting the wood chips or shreds.

In the sulfate process make-up chemical is added in the form of sodium sulfate to the concentrated black liquors, after which the make-up chemical is transformed to sodium sulfide in the smelt forming phase of the chemical recovery process and dissolved in the leach liquor during the smelt leaching step of the process. Smaller additions of sodium sulfate are usually made in a similar manner in those modifications of the soda process in which the caustic liquors are fortified with smaller amounts of sodium sulfide. The major portions of the make-up chemical in such modified soda processes, however, are added to the causticizing units in the form of soda ash which is causticized by the lime added thereto.

The sulfte types of processes utilize digesting liquors which usually contain alkali or alkaline earth suliites such as sodium or calcium suliites as components of the digesting liquors.

The so-called semi-chemical type of neutral suliite process involves a preliminary step wherein the wood is prepared for digestion by being de-barked and chipped or shredded. Thereafter the chips or shreds are digested under suitable digesting conditions in an aqueous sodium sulfte containing liquor which is rendered substantially neutral by sodium carbonate contained in the aqueous digesting liquor. In the semi-chemical processes, however, the digest of the chips is less drastic and, accordingly, when the digester is blown, the chips retain substantially their initial chip form. After the blow, the partially cooked digester product is mechanically reduced to pulp form, as, for example, in a fiberizer. Thereafter the pulp is washed and refined prior to its use on the paper machines.

alegre/o ab v3 It has been discovered that unbleached pulps prepared in accord with pulping processes which involve the digestion of ligno-cellulosic materials in liquors which contain compounds of sulfur are materially improved in their brightness characteristics if small amounts of certain organo-silicon compounds are added to the liquors employed in the digestive treatments. Our research and pilot plant work indicates that the advantages obtained by the use of the organo-silicon compounds are realized only when the digesting liquors include a sulfur compound as an active component of the liquor, such as found in the digesting liquors of the kraft, modified soda and suliite types.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. l is a schematic flow sheet illustrating the principal steps involved in alkaline wood pulping processes as modified in accord with the invention and which further illustrates the steps involved in the recovery of the chemical content of the caustic liquors employed therein.

FIG. 2 is a schematic flow sheet illustrating the principal steps involved in a semi-chemical neutral sulte process, as modied in accord with the invention described herein.

The organo-silicon compounds which may be employed as digester additives in accord with the invention include many different classes of compounds. However, all of the organo-silicon compounds which may be employed are characterized by at least one carbon-silicon linkage or bond in their representative formulae. The preferred class of digester additives are those polymeric organo-silicon compounds which are characterized by organo-siloxane groups (R-s:i-o-) in their formulae, the R being a hydrocarbon radical or simple substituted hydrocarbon radical such as exemplified in Formula I, hereinafter. Other classes of organosilicon compounds which are transformed under the digestion conditions to organo-polysiloxane materials may be employed as additives in lieu of the siloxanes. Thus, the benets of the invention are attributed to the presence of small amounts of organo-polysiloxane compounds in the digesting liquors during the digestive treatments of the ligno-cellulosic materials.

The organo-polysiloxanes to which the benefits of the invention are attributed include disiloxanes, trisiloxanes and higher polymeric forms of organo-siloxane compounds, and will be occasionally referred to herein as silicones or as polymeric organo-silicones, although there are instances in the art where such designations have been used more broadly to include all polymers containing repeating groups that contain Si atoms. The silicones or organo-polysiloxanes are typified in their polymeric forms by oxygen linked silicon atoms which may be structurally illustrated as follows:

sl-Outliand wherein there is at least one silicon-carbon linkage.

They may be prepared as liquids, semi-liquids, o1' as solids by Well known procedures, one of which involves hydrolysis and condensation of such organo-silicon compounds as the organo-silanes, organo-acryloxysiianes, organo-chlorosilanes and organo-alkoxysilanes. The following illustrates typical hydrolysis and condensation reactions showing the formation of a difunctional dimethylpolysiloxane from dichlorodimethylsilane wherein the organo-silanol, dimethylsilanediol, is formed.

(1) ([JH; (11H3 Cl-S-Cl -l- 2H2O HO-Si-OH -l- QHCl l hydrolysis CH3 CH3 dichlorodimethylsilane dimethylsianediol (dihydroxydimethylslane) (2) (IH-Ia (n -i- 1) I-IOSiOH e I Condensation CH3 dimethylslanediol (dihydroxydimethylsilane) a difunotional dmethylpolysiloxane The hydrolyzates formed as intermediates in the polymerization reactions are organo-silanols, and accordingly the silicones or organo-polysiloxanes may be considered as condensation products derived from organo-silanols. The functional polysiloxane formed from the condensation reaction may be end blocked in accord with known procedures or may be used as intermediates for copolymerization reactions with other compounds containing functional groups.

Typical monomeric organo-silicon compounds from which the organo-polysiloxane derivatives may be prepared by hydrolysis and condensation reactions involving the intermediate formation of organo-silanols may be represented by the following general formula:

(Formula I) wherein R is a hydrocarbon or a simple substituted hydrocarbon radical, usually having less than about 20 carbon atoms, and which is attached to the Si atom by means of a carbon-silicon linkage, and wherein the hydrocarbon radical may be alkyl, aryl, alkaryl, arylalkyl, alkenyl, cycloalkyl, cycloalkenyl, or a heterocyciic group, and the substituent may be a hydroxyl, alkoxy, aryloxy, halogen, carboxyl, amino, acetamino, sulfonic, nitro, or other simple substituent group.

X is a functional (hydrolyzable) group linked to the Si atom such as hydrogen, alkoXy, aryloxy, halogen, acyloXy, amino, alkylamino, silazanyl, sulfhydryl, or alkyl-thio group.

n is an integer selected from l, 2 and 3.

The intermediate organo-silanols formed by hydrolysis from the monomeric organo-silicon compounds depicted by Formula l may be represented as follows:

RnSi OH) (44,) (Formula Il) wherein R and n correspond to the designations of Formula I.

The organo-polysiloxanes derived by the hydrolysis and condensation reactions may be homopolymeric or copolymeric materials depending on whether one or more of the functional monomeric organo-silicon compounds are hydrolyzed together and may take the form of straight cyclic branched or cross-linked polymers depending upon the type or types of monomeric organo-silicon compounds employed in the reaction and further depending on the number of functional ,groups linked to the Si atoms thereof, as is weil known.

In lieu of utilizing the organo-polysiloxanes as digester additives, any of the compounds depicted by Formula I may be employed since they hydrolyze and condense under aqueous digestion conditions found in pulping processes of the type indicated herein and form polymeric organo-silicone materials. Other organo-silicon compounds which are transformed to the siloxanes under digesting conditions may also be added. For example it is well known that monoand polymeric organo-silicon compounds which have a silicon-silicon linkage less than rive carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl and isobutyl groups, and wherein n is an integer from 2 to about 2000. Especially satisfactory forms of organo-polysiloxane material are available commercially and are composed of a mixture of compounds l 5 .tro en silicon linka e in accord with Formula ITI wherein the Rs are methyl a m g g and wherein n is an integer averaging from 500 to 1200. l l, Homopolymeric siloxane compounds having such methyl N Sl substituents may be referred to as dimethylpolysiloxanes il. n sulfur linka e lo or as polydimethylsiloxanes.

or a S Ico g Only small amounts of the organo-silicon compounds S|i s*) need be added to the aqueous liquors employed for digestl ing the ligno-cellulosic materials to produce recognizable -n h ss f th un leached ul s. Us-

are'hydrolyzable and condense under alkaline conditions laalgnlnagd too seclre is benept Das been to Organo'polysiloxane materials'. Thus Such compounls 15 found to range from in excess of about l gram of addias. exempheflh by the Organo'sllazigles dho Orgo': tive per ton of ligno-cellulosic material (bone dry basis) per ton o igno-ce u osic materia one iy asis supolysuoxalle ad accordtlngly afg ecuve. addmt'esiallrf 20 jectecl to the digest.. Larger amounts may be employed afofd Wit tf Ingen (llnd, OPO ymerlfma erud; but usually the cost is excessive.' As between the organo- Wmch econlpobe .uff far t fel lgesmg C911 110mg s polysiloXanes and the organo-silicon compounds which a; ClopaymelS COHIaIHIHg S1 OX'H@ ftfupmag Sqorl are transformed thereto under digestion conditions, larger al/ @ne groupings may e use er 0 l* amounts of the latter are usuall re uired. compounds which may be benecially employed are It may be pointed out at thisypot that Organo po1y Such h'LeYO'POll/mefl mafnals as are formled by siloXane type compounds have inthe past been employed Condenslflf 0f COPD Ymellzug gwn?" f p0 yme for suppressing foam in the Washing stages of some kraft ofgano'slhcon dcomlounds afl/tlg ull lma hglolPS Wind mills. As such, and because of normal black liquor re- IDOllOmefS an P0 Ymes 0 e a Y i P e 0 C a cycle procedures, trace amounts of the organo-polysii esters wit e rec c e ac. i uor. uc trace pounds, such as diphenyldi-n-dodecylsilalle and 1am/1 anounts have producedI no recognizalle beneiits to the methylsilane, which normally are1 conidere? to dbe relglk'rgft pulp3 and accordingly thc small amounts ot organo- 1Ve1y- Stahl? ompounds have a S0 el hmm llo le silicon compounds employed in accord with the inventive effectlve f dd1t1VeS- Thus Compounds W C Conta@ S1 35 concept are to be distinguished from the trace amounts Caballe llnkages which inadvertently enter the digesters through the noi- |l 1 I. mal use of certain organo-silicon compounds as foam s*C-51") suppressants in the pulp Washing phases of the processes.

l l l Typical results which have been obtained in kraft type 40 cooks conducted on a pilot plant scale in accord with the mayhalsod .found to1-be eectweladduyesjth d. t f invention are set forth in Table I wherein it is evident Orgm) golgtslilgme lglm Olvirgl e lfohg that signicant and benecial increases in the respective brightness values of the unbleached pulps were obtained characztristic ptolymeric structure have been found to be by utilizing Various species of Organ0 si1icon type Com espe Y Sulta e pounds as digester additives. The percentage increases in brightness value reported in Table l represent the per- R R I centage increase in unbleached pulp brightness obtained R SI O SI O .S R in the respective cooks when compared with appropriate 1|l I IlL l| control cooks. All brightness values reported herein were measured with a standard photo-volt tester and in- (Formula HD dicate the percent reflectance of 460 millimicron wave n lengths wherein magnesium oxide is the standard 100% wherein, R may be hydrogen or an alkyl radical having reflectance value,

Table l [KRAFT COOKS] A. ORGANO-POLYSILOXANE TYPE MATERIALS Amount Percent Cook No. Additive (gm/t0n increase of bone in brightdrywood) ness value 99 A fluid (103 centistolres) end blocked diinctliylpoly- 10.5 11

siloxane. 100 Cyclic dimethyltctrasiloxane 21.5 7 98 A partially end blocked fluid polydimethylsiloxane conA 10. 5 7

taining small amounts (less than 6%) ol trifuuctional methylsilane. 175 Au end blocked dimethylpolysiloxane iluid 150 5 123 AiluilIrthylphenylpolysiloxane(lessthan30%phenyl 105 9 C011 en A fluid iethylphenylpolysiloxane (about 40% phenyl 105 2 C011 611 109 End blocked organo-siloxane iuid of general formulae-.. 10. 5 11 ['orr 'i ggii-l A.' 2 4 CH si-o-s-os-o-S' CH m LClHs |211 LCIHS in l( m Table I-Continued Amount Percent Cook No. Additive (gm/ton increase obone in brightdrywood) ness value 97 50-50 mixture of cyclic dimethyltetrasiloxane and a low 10. 5 2

molecular Weight iuid dimethylpolysiloxane. 131 A11 organo-polysiloxane fluid containing silanic hydro- 105 9 gen in a repeating group corresponding to Ill "I Sli-O- I CHe .la

114 An amylpolyslloxane resinous material 9 11 112 A highly condensed organo-polysiloxane resinous ma- 10 9 terial prepared from ethyltrichlorosilane. 117 A fully condensed organo-polysiloxane resinous ma- 3 2 terial prepared from trifunctional methylsilane and trifunctional plienylsilane with the latter predominating in amount. 108 Abloek copolymer correspondingto the general formulae- 10 11 O(R2SiO)- CH2UO\ R j. R-Si-O(R2SiO)q-(CnI-Izn0\ R /l O(RiSiO)r-(CH2O) R wherein (CnlrlznOM represents a mixed polyoxyethyleneoxypropylene block with the oxypropylene units predominating and z is less than about 30, (RzSiO) represents a dimethylpolysiloxane block and p, q and r are each 6, R is ethyl, and R is butyl. 101 Ablockcopolyrnercorrespondingtothegencralformulae 10.5 9

shown for cook 108 wherein R is ethyl R is methyl, R is butyl, p, q and r each equal G, z is about 30 and the ratio of oxyethylene units to oxypropylene units is about 17/13. n An end blocked methylethylpolysiloxane u1d 150 11 An end blocked nicthylpropypolysiloxanc lluid 150 5 Au end blocked rnethylbutylpolysiloxane fluid 150 7 An end blocked motliyltriiluoropropylpolysiloxane fluid. 150 5 A highly condensed organe-polysiloxane resinous ma- 150 5 terial prepared from trifunctional methylsilane. Dibonzyltetramethyldisiloxane. 1, 50() 2 Hcxaethyldisiloxane 1, 500 2 B. MONOMERIC TYPE ORGANO-SILICON COMPOUNDS Methyltrimethoxysilanc 105 15 Sodium methyl silanolate 10 4 Diphenyldichlorosilane.. 1, 500 6 Diphenylrnetbylsilane 1, 500 2 Diphenyldi-n-dodecylsilane 1, 500 4 Hcxaphenyldisilane 1, 500 S Vinyltriethoxysilane 1,500 5 Aminopropyltriothoxysilane 1,500 5 The compounds identied in cooks Nos. 10S and 101 digesters than heretofore possible. lt will be recognized are typical copolymers which contain siloxane groups by those skilled in the art that, during an alkaline digest and which are additives that produce an increase in the of wood chips, and especially When the liquor includes brightness of the pulps. Typical organosilicon comrecycled black liquor, that an appreciable amount of pounds which form polysiloxanes under digestion condi- 55 foam is produced which, if the digester contains an extions are identiied in the B portion of the table. cessive amount of caustic liquor, will escape from the The organo-silicon compounds may be added directly digester when the gases and turpentine are bled oil. to the digesters before or after the digesters are charged Foaming, accordingly, has heretofore limited the amount with chips and liquor, or may be added to the liquor or of liquor which may be employed for digesting a full Chips 13H01" t0 the Char-5mg 0f the dlgesem In baCn 60 digester charge of chips With the result that only a poroperations, it is preferable to add the compounds as solutions in a suitable solvent such as a hydrocarbon oil (eg. kerosene), or as emulsions or dispersione, so as to facilitate the admixture of the additives with the liquor during the digest. Only amounts of solvent or carrier need be employed which are suiiicient to effect solution, emulsiiication or dispersion of the additive as the case may be.

The additives not only increase the brightness of the pulps produced in accord with kraft digesting procedures, but also improve the color characteristics of the pulps. Generally the pulps appear Whiter and have improved texture, being composed of less shives, etc.

Another benciit derived through the use or the process of the instant invention lies in the ability when desired to employ greater quantities of digesting liquor in existing tion of the chips are actually submerged in the caustic liquor during the digest whereas the remaining portion of the wood chips is digested through Contact with the caustic in the foam. This leads to nonuniformity in the cooked pulp. The silicones have been found to appreciably minimize the amount of foam which is produced during the caustic digest of the Wood. As such, With existing digesting units, one is able to employ greater quantities of liquor in the digesting units than heretofore possible. This is beneiicial in that a greater proportion of the chips is thereby actually covered by the alkaline liquor during the digest and greater uniformity in the cook results. Larger quantities of caustic liquor also aid in neutralizing greater quantities of the fatty acids pres- 9 ent in highly resinous woods and thereby also enable greater soap recovery.

The improved color and brightness characteristics of unbleached kraft pulps produced in accord with the invention as compared to control pulps produced by digestive treatments conducted in the absence of the organopolysiloxanes are illustrated in Table ll.

The cooks identied in Table ll were conducted under closely controlled pilot plant kraft type cooking procedures utilizing a 22.5 liter mild steel batch digester which was heated by live steam injection. The chips employed in the cook were run-of-the-mill chips which included approximately 60% long leaf pine, 30% slash pine, and the balance being a mixture of short leaf pine, loblolly, pond and spruce. ln accord with the control procedures followed, the chips were classied and dried at about 220 F. to a moisture content of less than 10% prior to use. Only chips retained on a 1/2 screen and passing a 1 screen were employed in the cooks. For each cook, a sufficient amount of chips of known moisture content was charged to the digester to provide 3000 grams of bone dry wood subiect to the digest. Thereafter, a kraft mill liquor having a suldity (CS.) of about 30% (Canadian standard) and approximately the following analysis was charged to the digester in an amount sufficient to give the indicated EA. value:

A (total active alkali) equal .97 lbs/gal. (as NagO) Table 1I Amount Excita- Coolr Additive charged E.A.1 Cl2 Brighttion 3 No. (gm.) No ness 2 purity,

percent 141 Control None 9.0 24.0 12.0

166- Dimethyl polysilox- 0. 5 9. 0 20. l 16. 5

ane fluid.

140 Control None 12.0 13. 5 20. 3 43 161. Dimcthyl ploysilox- 0.5 12.0 12. 5 23. 5 42 ane fluid.

142 Control None 15.0 9. 6 23.7 40

162 Dimethyl polystlox- 0. 5 15.0 9. 9 27.0 39

anc fluid.

143 Control None 18. 0 7. 5 25.5 38

163 Dimethyl polysilox- 0. 5 18. 0 6. 8 29.0 37

ane fluid.

144 Control None 21. 0 7. 3 26. 3 40 14 Dimethyl polysilox- 0. 5 21.0 6. 2 29. 0 36 ane fluid.

1 Charging ratio, being the weight ot the eiective alkali charged to the digester expressed as a percentage oi the bone dry weight of wood charged th; 1lGgiiJc-ent reflectance of 460 millimicron wave lengths as compared to MgO standard white body having 100% reiiectance value.

3 Determined by tristimulus method, of International Commission on Illumination, Standard Illuminant C, as set forth in 1936 Edition of Handbook of Colorimetry, published by lVLLT. wherein the standard White light has an excitation purity of To compensate for the use of dry chips, 2 liters of Water was then added in accord with the control procedure followed. Thereafter the indicated amount of dimethyl polysiloxane compound was added to the digester as a solvent solution in 5 mls. of kerosene. The contents of the digester was then uniformly elevated to 90 p.s.\i.g. from atmospheric pressure during a period of about 45 minutes and then retained at full pressure for a period of about 1 hour and l5 minutes and blown to a blow tank. After screening and washing the unbleached pulp obtained from the digests, hand sheets were prepared in a standardized manner and tested for brightness and color characteristics. As shown in Table Il, each cook which contained an added dimethyl polysiloxane produced a pulp having a higher brightness value, and an excitation purity value which more closely approached the reference value for white light than the corresponding control cook.

The improvements in the color and brightness characteristics of the pulps are practically uninfiuenced by normal changes in the amount of chemical employed in the digests as shown in Table Il. Our investigations indicate yuid dimethylpolysiloxane materials, impart furthermore that normal differences in such digestion process variables as time, pressure and chemical concentrations have no appreciable eifect on the color and brightness differences which accompany the use of the organo-siloxane compounds. Instead such changes in the processing conditions produce the same result which would be expected, and the influence of the organo-silicon compounds appears to be independent of the changes.

The improvements in color and brightness of kraft pulps may be secured by adding the organo-polysiloxanes in small amounts which usually exceed about l gram of the additive per ton of wood (bone dry basis). However, we have also found that organo-polysiloxanes, such as the added strength properties to the refined pulps and that the maximum strength is produced when the organopolysiloxane materials are employed in the digestive treatments -in amounts which usually range from about 3 to about 15 grains of organo-polysiloxane compound per to-n of wood (bone dry basis).

Results from kraft cooks run under pilot plant control conditions have indicated an increase of as much as 15% in the mullen strength of pulps which have been refined in a Noble 8: Wood cyclic beater to a 400* ml. freeness value (as measured on a Green Freeness Tester) and produced by kraft cooks employing about 9 grams of added dirnethylpolysiloxane material per ton of chips (bone dry). Particularly suitable organo-polysiloxane compounds which impart good strength properties to the kraft pulps are the halogenated organo-polysiloxane cornpoiuids, as for example methyltrifluoropropylpolysiloxane compounds. Furthermore, Whereas kraft papers produced in accord with normal practices lose strength upon aging, we have found that such papers retain the original mullen strength properties after aging if the kraft pulps employed in the production of the papers are produced by kraft cooks employing dimethylpolysiloxane compounds as digester additive.

The kraft cooks reported in Table lil further illustrate the invention and show results obtained in cooks employing white liquor as the sole digesting medium and in cooks employing both white and black liquor for digestion purposes. Each cook was conducted in a 22.5 liter pilot plant type mild steel batch digester which was heated by live steam injection. The digester was rst charged to capacity with run-of-the-mill chips, which included approximately 60% long leaf pine and 30% slash pine, the balance being a mixture of short leaf pine, loblolly, pond and spruce. The white and black liquors employed were actual kraft mill liquors, the suliidity (C.S., Canadian standard) of the white liquor being about 27% and the total alkali content (A) being about l lb. of alkali (as NazO) per gallon. The black liquor was the same for both reported low yield cooks. The digester was charged in each cook to the indicated charging ratio (EA. value) by adding the indicated amounts of liquor. Thereafter in the appropriate cooks, the dimethylpolysiioxane material was added to the digester as a solvent solution containing the indicated amount of polysiloxane in a few ml. of kerosene.

The white liquor cooks were conducted with live steam injection wherein the pressure in the digester was uniformly elevated to psig. in a period of about 50 minutes and thereafter retained at full pressure for about l hour and 15 minutes. The contents of the digester was then blown to a blow tank, washed and then screened, on a .025 llat laboratory screen. Thereafter hand sheets were prepared of the unrened pulps and the indicated brightness values determined therefrom, an increase in brightness of about 13.5% being realized by the addition of dimethylpolysiloxane to the digester.

The low yield digests were conducted substantially in accord with the procedure followed in the white liquor cooks except that the pressure rise periods and full pressure periods were about 1 hour and 2 hours, respectively,

and the pressure employed during the full pressure period was 105 p.s.i.g. The brightness values obtained are set l2 The white liquor and black liquor employed in the respective digests had the following characteristic analysis:

Table Ill [SULFATE COOKS] l l Amount Liters of Liters of Total 2 Screen 3 Bright- Cook No. Type Cook Additive charged E.A.,1 white black yield, yield. C12 No. ness,4

(gm.) percent liquor liquor percent percent; percent charged charged 103 White liquor kraft cook- (Control) 13.1 6.81 None 51.9 40.2 12.5 22 99 do Diniethyl polysiloxane 13.2 6.81 None 53.7 41.1 25

uid (103 ctsk.). 89 Low yield kraft cook (Control) 13.3 6.98 .53 47.2 39.8 7.2 22

with black liquor. 90 do Dnehyl polysiloxane .1 13.3 6. 98 .53 47.4 40.0 27

1 Charging ratio, being the Weight of the ei'lcctive alkali charged to the digcstcr expressed as a percentage of the bone dry Weight of wood charged thereto.

2 Expressed as the percentage of bone dry wood chalrged to the digester.

3 Expressed as the percentage ol the total pulp yielt 4 Percent reilectance of 460 niillirnicron wave lengths as compared to MgO standard White body having 100% reflectance value.

forth in the table and indicate an increase in brightness of about 22% in the low yield cook employing the dimethyl polysiloxane additive.

The material set forth in Table IV further exemplines this invention by comparing three separate mill scale kraft-type sulfate digests. Run A was a normal high yield kraft-type digest employing black liquor. Run B Was a normal low yield kraft-type digest employing black liquor and Run C was a kraft-type digest employing white liquor wherein a dimethylpolysiloxane material was added to the digester in accord with the inventive concept. Each of the digests was conducted utilizing 54,000 lbs. of wood chips wherein the wood was southern pine and accordingly of a highly resinous nature.

Table IV Run A Run B Run C Digester charge Normal Normal New digest,

digest, digest, high yield high yield low yield Chips 1 (lbs.) 54,000 54,000. White liquor charge (gal.) l0,200 10,400.

Active alkali (lbs.) (as 8,400 8,500.

N 0,20) Black liquor charge (gal.) 800 N one. Active alkali (lbs.) (as 130 N one.

N aaO) Total liquor charge (gal.) 11,000 10,400.

Total active alkali (lbs.) ,530 8,500.

(as NasC). Dimethylpolysiloxane 2 None 3 ez. Digester Conditions:

Steam dilution 4,470 gal 4,470 gal 3,890 gal. Ternp. .FJ-Press4 331-105 331-105 B20-90.

p.s.i. Pressure rise period 65 min 65 min 55 min. Full pressure period 60 min. Pressure reducing pemin.

riod. Yield:

Total pulp yield (per- 53.

cent of wood).3 Rejects (percent of total 20.

pulp yield).4 Soap (percent of Wood) 3 5.02. Tall oil (percent of 2.51.

wood).3 Turpeutine (gal.) 42. Pinene content (per- 88-90.

cent. Pulp characteristics:

Color Lighter than Run A. Chlorine number 5 14- 12-13. Quality of pulp Hard Solter than Run A.

l Weight reported as bone dry wood.

2 Average n=750 (see Formula HI). Added as a kerosene solution containing 1.280 lhs. of dimeth ylpolysiloxane material per gal. of kerosene.

3 Based on weight ol hone dry weed charged to digester.

4 The amount of rejects is determined 'oy the amount of pulp retained on a .025 fiat screen.

5 Based on total yield.

1 Reported as lbs. of equivalent NMO per gal.

With reference to Run A, it will be seen that 8,550 gals. of white liquor having an active alkali content of 7,100 lbs. was charged to the digester together with 2,450 gals. of black liquor having an active alkali content of 390 lbs. The total liquor charged to the digester was 11,000 gals. of liquor which had a total alkali content of 7,490 lbs. The digest of the chips in the alkaline liquor was accomplished in the absence of any added organo-silicon cornpound by live steam injection wherein the temperature of the digester was raised to 331 F., or a pressure of psi., over a period of 65 minutes. Thereafter the chips were digested at full pressure for a 45 minute period and the digester thereafter relieved and blown to the blow tank over a 20 minute period. The amount of dilution by the steam injected amounted to 4,4-70 gals.

From the information set forth in the table under Run A it will be seen that the digest was a typical high yield kraft digest wherein the total pulp yield was about 53% of the wood charged. Thirty-four percent of the pulp secured from the blow tank was retained on a .025 ilat screen and needed refining prior to use on the paper machines. The amount of soap obtained was 4.6% of the wood charged and the amount of tall oil recovered was 2.08% ot the wood charged. About 42 gals. ot turpentine were recovered during the digest, and the turpentine had a pinene content of about 5S-86%. The process was productive of a normally hard kraft-type pulp which was dark in color and which had a chlorine number between 14 and 15.

Run B was a typical low yield kraft sulfate digest in which 54,000 lbs. of chips were digested, in 11,000 gals. of a mixture of White and black liquor having, respectively, 8,400 lhs. and 130 lbs. of active alkali content. The digest was also conducted at a pressure of 105 psi. which was gradually secured by raising the temperature to 331 F. over a 65 minute period by live steam injection. Thereafter the contents of the digester was maintained under full pressure for minutes after which period the pressure was relieved over a 20 minute period and the contents blown to the blow tank. Like Run A, no organo-silicon compounds were employed in the digest.

The digest in Run B was a typical low yield kraft digest lffl chips thereafter classified and oven dried at about 220 F. Only chips passing a l" screen and retained on a 1/2" screen were utilized. The liquors employed were synthetic liquors, as opposed to mill liquors, and conwherein 46% of the wood remained undigested and in 5 sisted of aqueous solutions of sodium hydroxide and sothe form of a fibrous pulp and wherein the soap, tall oil dium sulfide having total alkali contents of about 1 lb. of and turpentine recovered were substantially the same as total alkali (as NaZO) per gallon of liquor, and had the in Run A. The pulp secured was lighter in color than indicated suldities (C.S.). The digester employed was that secured in Run A andthe pulp was characteristically a 22.5 liter mild steel pilot plant type batch digester considerably softer than that obtained in Run A, and had which was charged in each cook with chips having a achlorine number between 6 and 7. bone dry weight of 3000 grams and a known moisture Run C was also a digest of 54,000 lbs. of wood chips content of less than about 10% moisture. The amount in caustic liquor. ln this run the caustic liquor comof synthetic liquor charged to the digester in each cook prises 10,400 gals. of white liquor which contained 8,500 was sufficient to give an EA. value of 16%. After the lbs. or" active alkali. In accord with the invention 3 15 liquor and chips were charged to the digester an approounces of a dimethylpolysiloxane iluid material was added priate amount of water was added in accord with the to the digester, the silicone being first dissolved in a small control procedures to bring the total volume of liquid amount of kerosene and added to the digester as a solvent in the digester, including contained chip moisture, to 6 solution of the silicone material in kerosene. The diliters. ln the appropriate cooks, the indicated amount gest of the wood was carried out at a lower pressure 20 of organopolysiloxane material was then added to the and temperature than either of the digests set forth in contents of the digester. The digests were all conducted Runs A and B which, but for the presence of the addiat 100 p.s.i.g. utilizing live steam injection, a period of tive, would normally cause a darker pulp to be produced. one hour and 5 minutes being employed to uniformly The temperature for Run C was elevated to 320 F. raise the pressure in the digester from atmospheric to by injecting live steam over a period of minutes, 25 full pressure. Thereafter, the digests were conducted at after which the wood chips were subjected to full presfull pressure for a period of one hour and 55 minutes. sure for a period of minutes. Thereafter the pres- At the completion of the full pressure period, the consure on the digester was relieved over a 20 minute period tents of the digesters were blown to a blow tank and as the chips were passed to the blow tank. the pulps screened, washed and hand sheets prepared in The amount of pulp obtained was 53% of the wood 30 a standard manner. charged to the digester which it will be understood The yields, chlorine numbers and brightness values corresponds in amount to that normally secured in a reported in Table V are averages for two cooks conhigh yield kraft sulfate digest such as illustrated in the ducted in accord with the aforementioned procedure. table under Run A. However, only 20% of the pulp It is evident from Table V that the addition of the disecured from the blow tanks needed reiining. Furtherv35 methylpolysiloxane compounds caused an increase in the more, it will be noted that the amount of soap recovered brightness of the unbleached pulps. Furthermore, in in the subsequent steps of the process was 5.02% of each cook where an organo-polysiloxane was employed, the wood charged to the digester and that the amount the pulp produced was considered to be of finer texture of tall oil recovered increased by better than 20% as and of an improved quality.

T able V [MoDirrED SODA Cooks] Amount C.S.1 Litcrs of Total2 Screen3 C12 No. Bright- Cook No. Type cook Additive charged percent liquor yield, yield, percent ness, 4 (gm.) charged percent percent percent 258-259 Soda cooks (1% sulfidity)-. (Control) None 1.35 3. 89 47.7 44.5 12.2 26.7 26o-261 V-de Dimethylpolysiloxane fluid. 5.0 1.35 3.89 45.6 43.8 11,4 28,2 26a-26s soda cooks (6% sulfidity) (Control) None 6.2 4.23 44.5 43,0 6.5 29,0 264-265 do Dimethylpolysiloxane fluid. 5.0 6.2 4. 23 44.6 43.1 6.2 30,0

1 Sultidity (Canadian standard). 2 Expressed as the percentage of 3 Expressed as the percentage 0l the total pulp yield.

4 Percent reilectance of 460 millimicron wave lengths as compared to compared to the amount recovered in either Run A or B. The amount of turpentine recovered was substantially the same as that recovered in Runs A and B. However, a substantial increase in the pinene content was realized as shown in the table. In addition to the foregoing the color of the pulp secured in Run C was lighter than either of the pulps secured in Runs A and B and the quality or texture of the pulp was comparable to or better than that obtained in Run A. That is surprising in view of the fact that the chlorine number was between 12 and 13 thereby indicating a significant lignin content.

Typical results which have been obtained by using the organo-silicon compounds as digester additives in other processes which employ liquors containing sulfur compounds as active components of the liquor are shown in Tables V and VI.

The modiiied soda cooks set forth in Table V were conducted under closely controlled pilot plant digesting conditions wherein the chips employed were from long leaf yellow pine logs which were chipped green, and the hone dry wood charged to the digester.

MgO standard White body having 100% reflectance value.

than 10%.

200 grams of Na2CO3.

Results obtained in pilot plant semi-chemical pulping processes utilizing so-called neutral sulte type liquors for digestion purposes are set forth in Table VI. The cooks reported therein were conducted in a 22.5 liter stainless steel batch type digester under closely controlled pilot plant type conditions. The chips employed were obtained from poplar logs which were chipped green, classified and dried to a chip moisture content of less Only chips passing a 1" screen and retained on a 1/2 screen were subjected to the cooking operations. For both cooks reported in Table VI, the digester was charged with chips having a bone dry weight of 3,000 grams and with 5.8 liters of an aqueous digesting solution containing 750 grams of Na2SO3 and In cook No. S-54 the dimethyl polysiloxane material was charged to the digester immediately after the chips and liquor had been added thereto. The respective digests were carried out at p.s.i.g. utilizing live steam injection, 50 minutes being the time period allotted for uniformly elevating the pressure from atmospheric to the full digestion pressure, and

Table Vl [NEUTRAL SULFITE COOKS] Amount Total Cook Type Additive charged yield, C12 No. Bright- No. Cook (gm.) percent ness S-51. Neultfral (Control) None 57.0 16.2 83

su te. S-54 do. A dimethyl- 5.0 55.7 13.0 46

polysiloxane 1luid.

From the foregoing it is evident that substantial improvements in the pulps result by employing small -amounts of organo-polysiloxanes as digester additives in processes employing digesting liquors which contain sulfur compounds as active components of the liquor. Coniferous and deciduous woods, as well as other lignocellulosic materials may be digestively treated in accord with the invention. However, the use of the organopolysiloXane additive for the digestive treatment of coniferous woods is particularly advantageous since such woods contain resinous foam-producing materials and the polysiloxane compounds additionally function as foam vSuppressors during the digestive treatment.

FIG. 1 schematically illustrates the basic steps in an yalkaline wood pulping process as modified in accord with the herein described invention, and further illustrates the basic steps involved in the recovery of the alkali content of the black liquor. With reference to the figure, the wood 36 is prepared for digestion in a preparation step illustrated at 1, by being de-barked and cut into small chips or shreds the bark being removed and discarded as at 37. The chips 38 are then loaded into the digester, schematically illustrated at 2, and the selected amount of organo-silicon material 3 (preferably about 3 to l5 grams of dimethylpolysiloxane dissolved in a small amount of hydrocarbon oil such as kerosene), added to the digester 2 wherein the additive is mixed with caustic liquor 4 for digesting the chips. digester 2 to bring the temperature of the contents thereof up to the desired point and the turpentine d is removed from the digester during the digest of the wood chips in a manner well known to those skilled in the art. After the digest of the wood chips has been completed the pressure is relieved in the digester 2 as the contents of the digester is passed, as indicated by arrow 7, to a blow -tank 8. Thereafter the pulp and spent caustic liquor are passed as indicated at 9 to a pulp refining phase of the pulping process which phase is indicated at it?. In this phase of the pulping process, the pulp is subjected to a mechanical pulping action to reduce the rejects, as much as practical, to a usable pulp. The pulp is then passed as indicated at l2 to the pulp washers shown schematically at 13. Water 14 is fed to the pulp washer to wash the pulp free of the caustic liquor. The pulp is removed and separated from the caustic liquor as at l5, and is then screened as at l1 to separate the shives and knots therefrom, whereafter it may be processed into paper. The caustic liquor from the washer units i3, termed black liquor i6, is thereafter usually stored in a black liquor tank, shown at 17, prior to being treated for the recovery of the alkali content thereof. As shown at 18 a portion of the black liquor from the storage tank il? may be removed and combined with the white liquor i9 Live steam as at is added to the d lb produced in lthe recovery steps and which is stored in tank 2t). The combined liquors d may then be used in digesting a subsequent charge of chips in digester 2. Preferably, however, the black liquor in storage tank i7 is all subjected to a chemical recovery treatment and the chips are digested in white liquor only.

The black liquor is passed from the black liquor storage tank 17 as shown by means of arrow 318' to evaporation units 19 wherein the black liquor is concentrated and the steam removed as at Zit. Soap 2l may also be removed in the conventional manner during the evapora- `tion step after which the concentrated black liquor indicated at 22 is passed to a suitable furnace 23 wherein it is burned with air to form a smelt as shown at 24.

Make-up chemical in the form of sodium sulfate, shown at 25, may be combined as, for example, in the sulfate process, with the evaporator efiiuent prior to the concentrated liquor being subjected to the burning operation in furnace 23. The smelt 2li from the furnace 23 is then treated in a leaching unit 26 with water 27 to leach out the water soluble chemicals in the smelt 2li which coinprise principally sodium carbonate and sodium sulfide. rf'he aqueous solution secured from the leaching unit 26 and which is conventionally known as green liquor is then passed as illustrated at 27 to -a causticizing unit 28 wherein the sodium carbonate content of the green liquor is reacted with lime 29 to form caustic soda (NaOH) and insoluble calcium carbonate or lime mud.

Where the instant invention is utilized in the modified forms of the soda process, soda ash 3@ may be added to the causticizing unit 28 as make-up chemical and causticized by lime 29 together with the sodium carbonate content of the green liquor Z7.

The causticizer efiiuent 31 is passed to a clarication unit 32 in which the lime mud 33 is separated from the white liquor produced in the causticizing unit. To facilitate the removal of the lime mud a flocculating agent 34 such as starch may be added to the clarification unit. The white liquor is then passed as exemplified by line 35 to white liquor storage tank 2d after which it is employed for subsequent chip digesting purposes.

FIG. 2 is a schematic drawing illustrating the more important steps in a semi-chemical pulping process utilizing a neutral sulfite digestion liquor. The wood 39, such as poplar, is first prepared for digestion, as schematically illustrated at dit, by being de-barked and chipped, the bark being separated as at 41 and the chips 42 being charged to the digester which is illustrated at 43. Neutral sulfite liquor 44- is then charged to tne digester 43 and an appropriate amount of dimethylpolysiloxane material i5 is also charged thereto, preferably as a solution thereof in a small amount of hydrocarbon oil such as kerosene. Next the digester is heated to an appropriate pressure by the injection of steam as at 4.16 and after a suitable digestion period the contents of the digester are blown to a blow tank 47 as indicated by arrow 4S. The steam released during the blow is passed off from the blow tank as at 49. From the biow tank 47, the digester product is passed as by arrow d@ to a iiberizer 51 in which the digester product is mechanically reduced to a pulp 52. The pulp 52 is thereafter washed in a washer 53 by water 54 and the brown liquor 55 separated from the washed pulp 56 and delivered to a chemical recovery unit' (not shown). The washed pulp 5d is then refined in refiners 57 from which the refined pulp $8 is delivered to the paper mill for use in making paper.

it will be understood by those skilled in the art that very few of the organo-polysiloxane compounds have been isolated as individual compounds and that the term compound as used herein with reference to polymeric materials may include mixtures of respective polymeric cornpounds.

While only a'certain preferred embodiment of this invention has been shown and described by way of illustration, many modifications will occur to those skilled in the art and it is, therefore, desired that it be understood l? that it is intended in the appended claims to cover all such modications as fall within the true spirit and scope of lthis invention.

This application is a continuation-in-part of our copending application Serial No. 823,249, tiled lune 26, 1959, entitled Wood Pulping Process, now abandoned.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is:

l. A method of increasing the brightness value of pulped material produced in a pulping process which process includes a step of digestively treating ligno-cellulosic material in aqueous digesting liquor having an active sulfur containing digesting component, comprising adding an organo-polysiloxane compound to said digesting liquor and digestively treating the ligno-cellulosic material in the digester in the presence of said polysiloxane compound, the addition of said additive compound being in an mount to provide from about one gram to about 50 grams of additive compound per ton of ligno-cellulosic material (bone dry basis) subjected to digestive treatment therein.

2. The method of claim 1 wherein said organo-polysiloxane material comprises dimethyl-polysiloxane.

3. A method of increasing the brightness value of pulped wood produced in a pulping process which process includes a step of digestively treating wood in an aqueous digesting liquor having an active sulfur containing digesting component, comprising adding to the digester an organo-silicon material selected from the group consisting of organo-polysiloxane compounds and organosilicon compounds that are hydrolyzable and condensable to organo-polysiloxane compounds under the conditions of the digestive treatment, and digestively treating the wood in the digester in the presence of said organo-silicon material, the addition of said organo-silicon additive material being in an amount to provide from about one gram to about 50 grams of additive material per ton of wood (bone dry basis) subjected to the digestive treatment therein.

4. The method of claim 3 wherein the organo-silicon material comprises dimethyl-polysiloxane.

5. A method of increasing the brightness value of pulped wood produced in a sulfate process of pulping wood which process includes a step of digestively treating wood in a digester, comprising adding to the digester an organo-silicon material selected from the group consisting of organo-polysiloxane compounds and organo-silicon compounds that are hydrolyzable and condensable to organo-polysiloxane compounds under the conditions of the digestive treatment, and digestively treating the wood in the digester in the presence of said organo-silicon material, the addition of said organo-silicon additive material being in an amount to provide from about one gram to about grams of additive material per ton of wood (bone dry basis) subjected to the digestive treatment therein.

6. The method of claim 5 wherein the organo-silicon material comprises organo-polysiloxane material.

7. The method of claim 5 wherein the organo-silicon material comprises dimethyl-polysiloxane material which is added to the digester in an amount in the range of from about three grams to about tifteen grams thereof per ton of wood (bone dry basis) subjected to the digestive treatment therein.

8. The method of claim 5 wherein the organo-silicon material comprises halogenated organo-polysiloxane material.

9. A method of increasing the brightness value of pulped Wood produced in a modified soda process of pulping wood which process includes a step of digestively treating wood in a digester, comprising adding to the digester an organo-silicon material selected from the group consisting of organo-polysiloXane compounds and organo-silicon compounds that are hydrolyzable and condensable to organo-polysiloxane compounds under the conditions of the digestive treatment, and digestively treating the wood in the digester in the presence of said organo-silicon material, the addition of said organo-silicon additive material being in an amount to provide from about one gram to about 50 grams of additive material per ton of wood (bone dry basis) subjected to the digestive treatment therein.

10. The method of claim 9 wherein said organo-silicon material comprises dimethyl-polysiloxane material.

11. A method of increasing the brightness value of pulped wood produced in a semi-chemical process of pulping wood which process includes a step of digestively treating wood in a digesting liquor having an active sulfur containing component, comprising adding to the digester an organo-polysiloxane material, and digestively treating the wood in the digester in the presence of said organo-polysiloxane material, the addition of said organopolysiloxane additive material being in an amount to provide from about one gram to about 50 grams of additive material per ton of wood (bone dry basis) subjected to the digestive treatment therein.

Casey: Pulp & Paper, vol. I, published by Interscience Pub., New York, 1952, page 431.

Stephenson: Pulp & Paper Manufacture, vol. I, pub. by McGraw-Hill, New York, 1950, page 551. 

1. A METHOD OF INCREASING THE BRIGHTNESS VALUE OF PULPED MATERIAL PRODUCED IN A PULPING PROCESS WHICH PROCESS INCLUDES A STEP OF DIGESTIVELY TREATING LIGNO-CELLULOSIC MATERIAL IN AQUEOUS DIGESTING LIQUOR HAVING AN ACTIVE SULFUR CONTAINING DIGESTING COMPONENT, COMPRISING ADDING AN ORGANO-POLYSILOXANE COMPOUND TO SAID DIGESTING LIQUOR AND DIGESTIVELY TREATING THE LIGNO-CELLULOSIC MATERIAL IN THE DIGESTER IN THE PRESENCE OF SAID POLYSILOXANE COMPOUND, THE ADDITION OF SAID ADDITIVE COMPOUND BEING IN AN AMOUNT TO PROVIDE FROM ABOUT ONE GRAM TO ABOUT 50 